PET has been widely used in clinical examination and disease diagnosis in recent years. A detector is an important component of a PET device. When the PET device performs a scan, the detector and/or other components of the PET device may generate heat, which may cause an increase in temperature, and affect the performance of the PET device or a portion thereof. The increase of temperature may have an impact on the operation of the detector. Thus, it is desirable to develop heat transfer and cooling systems and methods for the PET device that may solve the above mentioned problem.